by
Stewart, James; Redlin, Lothar; Watson, Saleem

Answer

$A= \frac{18x}{t}$

Work Step by Step

Since $A$ is directly proportionaI to $x$ and inversely proportional to $t$, we have:
$A=\frac{kx}{t}$
We are given: $A=42$ and $x=7$ and $t=3$, so we have:
$42= \frac{k*7}{3}$
$k=42*3/7=18$
So the equation is:
$A= \frac{18x}{t}$